Displacement detection device and lens barrel

ABSTRACT

A displacement detection device which detects a displacement of a movable member which is provided so as to be displaceable with respect to a fixed member, comprises: a scale that is provided as a unit with the movable member; a displacement detection section that detects a displacement of the scale; a support member that supports the displacement detection section in a state in which the displacement detection section is able to shift in a direction which is substantially perpendicular to a contact plane where the displacement detection section contacts with the scale at a contact position between the displacement detection section and the scale and in which shifting in a direction other than the direction substantially perpendicular to the contact plane is restricted; and a pressure application member that applies a pressure to the displacement detection section towards the scale.

The present invention is based upon Japanese Patent Application2001-340298 filed upon Nov. 6, 2001, and hereby incorporates the contentthereof by reference.

TECHNICAL FIELD

The present invention relates to a displacement detection device whichdetects a displacement of a movable member and to a lens barrel whichcomprises the displacement detection device.

BACKGROUND ART

With many mechanical devices, the displacement and the speed of amovable member have been detected minutely as information for performingfeedback control or the like in recent years. For example, with a lensbarrel of an auto focus camera, a focus cam mechanism is providedinternally which converts the rotational drive force of an electricmotor or the like into a linear drive force, so as to shift the focusinglens. In Japanese Laid-Open Patent Publication No. 2000-205808, there isdisclosed a displacement detection device which detects the rotationaldisplacement of a rotating tube included in such a focusing cammechanism which is provided to this type of lens barrel.

This related art device comprises a magnetic pattern which is disposedupon the exterior peripheral surface of the lens barrel along itscircumferential direction, and a magnetoresistive sensor (MR sensor)which is made to contact with the magnetic pattern in order to detectthe rotational position of the movable barrel. The MR sensor issupported in a holder, and is biased or pressed via the holder towardsthe magnetic pattern by the spring force of a pressure spring. It isarranged that the MR sensor is capable of swinging with respect to thepressure spring.

However, with this type of related art device, since it is necessary forthe holder to be held by the pressure spring with a certain degree offreedom, accordingly there is a problem of deterioration of detectionaccuracy being caused due to the occurrence of play between the pressurespring and the holder.

DISCLOSURE OF THE INVENTION

The present invention provides a displacement detection device, a lensbarrel, and a camera, with which a scale can be read accurately.

A displacement detection device according to the present invention,which detects a displacement of a movable member which is provided so asto be displaceable with respect to a fixed member, comprises: a scalethat is provided as a unit with the movable member; a displacementdetection section that detects a displacement of the scale; a supportmember that supports the displacement detection section in a state inwhich the displacement detection section is able to shift in a directionwhich is substantially perpendicular to a contact plane where thedisplacement detection section contacts with the scale at a contactposition between the displacement detection section and the scale and inwhich shifting in a direction other than the direction substantiallyperpendicular to the contact plane is restricted; and a pressureapplication member that applies a pressure to the displacement detectionsection towards the scale.

It is preferable that the support member is formed as a thin platemember with an elastic characteristic. It is preferable that one end ofthe support member is fixed to the fixed member, and another end of thesupport member supports the displacement detection section. It ispreferable that the support member is arranged so that a longitudinaldirection thereof extends along a direction of shifting of the scale.

It is preferable that the pressure application member applies thepressure substantially in a center of the contact position of thedisplacement detection section.

It is preferable that a portion of the scale which contacts with thedisplacement detection section is a tube surface, and that the supportmember is provided on the contact plane or in the vicinity of thecontact plane, and is arranged substantially parallel with the contactplane.

The support member may comprise a rigidity reduction section at aportion of the support member which bends when the displacementdetection section shifts in the direction substantially perpendicular tothe contact plane. It is preferable that the rigidity reduction sectionis provided in the vicinity of a substantial center of the supportmember. The rigidity reduction section may be a hole portion which isprovided in the support member.

It is preferable that the pressure application member does not applyforce to the displacement detection section and does not restrict aposition of the displacement detection section in a direction other thana pressure application direction in which the pressure applicationmember applies the pressure to the displacement detection sectiontowards the scale. It is also preferable that the pressure applicationmember is arranged so that a longitudinal direction thereof extendsalong a direction of shifting of the scale.

It is desirable that the scale is a magnetic scale whose differentmagnetic polarities are arranged alternatingly along a shiftingdirection, and that the displacement detection section comprises amagnetoresistive sensor that detects a magnetism of the magnetic scale.The displacement detection section may include a gap regulation memberthat regulates a gap between the magnetoresistive sensor and themagnetic scale, and the gap regulation member may be provided on a sideof the magnetoresistive sensor which faces the magnetic scale.

The displacement detection section may comprise a convex portion at aportion thereof to which the pressure is applied by the pressureapplication member.

A lens barrel according to the present invention, comprises: aphotographic optical system; a fixed member that is to be fitted to aphotographic device main body; and a displacement detection deviceaccording to any one of claims 1 through 14, wherein: the displacementdetection device detects a displacement of a movable member that rotateswith respect to the fixed member to drive at least a portion of thephotographic optical system.

A camera according to the present invention comprises: a camera mainbody, and a lens barrel according to claim 15.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a lens barrel which is provided with adisplacement detection device according to a first embodiment of thepresent invention.

FIGS. 2( a) and 2(b) are figures showing the displacement detectiondevice according to the first embodiment.

FIG. 3 is an enlarged view showing the surroundings of an MR sensor.

FIG. 4 is a perspective view of a lens barrel which is provided with adisplacement detection device according to a second embodiment of thepresent invention.

FIGS. 5( a) and 5(b) are figures showing the displacement detectiondevice according to the second embodiment.

FIG. 6( a) is a figure showing a support plate in the first embodiment,while FIG. 6( b) is a figure showing a support plate in the secondembodiment.

FIGS. 7( a) through 7(d) are figures showing the contact situationbetween a holder and a scale.

FIG. 8 is a figure for explanation of the case in which the supportplate of the second embodiment is provided in a position which isidentical to that of the support plate in the first embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

First Embodiment

In the following, a displacement detection device and a lens barrelaccording to the first embodiment of the present invention will bedescribed in detail.

FIG. 1 is a perspective view showing a lens barrel 100 which is equippedwith a displacement detection device according to the first embodimentof the present invention. And FIGS. 2( a) and 2(b) are figures showingthis displacement detection device according to the first embodiment.FIG. 2( a) is a figure showing the displacement detection device fromthe outer peripheral side of the lens barrel 100, while FIG. 2( b) is afigure showing its appearance as observed from the side of a subject tobe photographed (the −Y axis direction). It should be understood thatfor a purpose of illustration a coordinate system is provided whichconsists of an X axis, a Y axis, and a Z axis, as shown in FIGS. 2( a)and 2(b). In the following, the same coordinate system will be used forFIGS. 1 through 5. Moreover, it should be understood that the lensbarrel 100 is fitted to a camera main body by a bayonet mount or thelike which is not shown in the figures, so that the +Y axis direction istowards the camera main body.

A displacement detection device according to the first embodiment of thepresent invention is provided to the lens barrel 100 of the camera, andis a magnetic encoder which detects displacement of a rotating tube 105which rotationally shifts relative to a fixed tube 103. The displacementdetection device comprises a scale 130, a MR sensor 147, a holder 145, apressure spring 141, a support plate 161, a spacer film 149, a flexibleprinted circuit 151, and the like.

The fixed tube 103 has a bayonet mount, and is a fixed member which isfixed to the camera main body via this bayonet mount. This fixed tube103 also comprises a seat 103 a for fixing a support plate 161 whichwill be described hereinafter, and a seat 103 b for fixing the pressurespring 141.

The rotating tube 105 is rotatable with respect to the fixed tube 103,and is a movable member which rotates by receiving drive force from adrive source not shown in the drawings and moves a lens group not shownin the figures through a cam mechanism or the like.

The scale 130 is fixed by adhesion against the outer peripheral surfaceof the rotating tube 105, and is a magnetic scale upon which a scale isprovided by magnetization along its circumferential direction. At thescale 130 magnetic poles of different polarity are arrangedalternatingly along the shifting direction of the scale 130.

The MR sensor (magnetoresistive sensor) 147 is a detection element mainbody which is adhered to the holder 145 and which detects the magnetismof the scale 130.

FIG. 3 is an enlarged figure showing the vicinity of the MR sensor 147shown in FIG. 2( b). The flexible printed circuit 151 is connected tothe MR sensor 147, and is made so that the magnetic signal which isdetected by the MR sensor 147 is transmitted to a lens CPU not shown inthe figures. This lens CPU calculates the rotational displacement of therotating tube 105 based upon this magnetic signal.

The spacer film 149, which has a low coefficient of friction, is stuckto the scale 130 side of the MR sensor 147 and the flexible printedcircuit 151. Due to this it is ensured that, when the MR sensor 147 isproperly contacted against the scale 130, the gap between them both isset to the most appropriate gap. As shown in FIG. 3, the contactposition when the scale 130 and the spacer film 149 are properlycontacted together is called “S”.

The holder 145, along with holding the MR sensor 147, also is supportedby the support plate 161. This holder 145 is provided with a sphericalconvex portion 145 a upon its opposite side from its portion whichsupports the MR sensor 147, in other words upon its +Z side.

It should be understood that the holder 145, the MR sensor 147, thespacer film 149, and the flexible printed circuit 151 and so onconstitute a displacement detection section.

The pressure spring 141 is a pressure application member which appliespressure to the holder 145 and the MR sensor 147 towards the scale 130.At its one end, this pressure spring 141 is fixed by screws 144 to theseat 103 b, and, at its other end, it contacts the convex portion 145 a,thereby applying pressure to the holder 145 and the MR sensor 147 withrespect to the scale 130. Accordingly, this pressure spring 141 does notapply any force to the holder 145 and the MR sensor 147 in any directionother than this direction of pressing the holder 145 and the MR sensor147 towards the scale 130 (i.e. the −Z direction). Furthermore, thepressure spring 141 does not restrict the position of the holder 145 andthe MR sensor 147 in any direction other than the Z direction.

The support plate 161 is made of an elastic material which is of verythin plate shape and it is a support member which supports the holder145. In this embodiment, the support plate 161 and the holder 145 arefixed to each other with adhesive.

When a plane parallel to the XY plane, i.e. perpendicular to the Z axis,which passes through the position S in which the spacer film 149contacts the scale 130 is taken as a contact plane, the support plate161 is arranged substantially parallel to this contact plane. One end ofthis support plate 161 is fixed to the seat 103 a of the fixed tube 103by screws 143, while its other end is fixed to the holder 145.

Although this support plate 161 is made of an elastic material, it doesnot generate any pressing force (i.e. it is not bent and thus a springforce is not generated) in the situation in which the MR sensor 147 iscontacted against the scale 130 in the correct position.

Since the support plate 161 is made of a thin plate shaped material, itaffords almost no support in the direction (the Z axis direction) whichis substantially perpendicular or orthogonal to the contact plane.Accordingly, the holder 145 can be shifted in the Z axis direction by asmall force. On the other hand, since the rigidity of the support plate161 in directions within the contact plane is high compared to itsrigidity in the Z axis direction, so that it is difficult for thesupport plate 161 to be deformed in those directions, accordingly thesecure support of the holder 145 in directions within the contact planeis assured.

As shown in FIGS. 2( a) and 2(b), the seat 103 b to which the pressurespring 141 is fixed and the seat 103 a to which the support plate 161 isfixed are separated from each other and are disposed on either side (the+X side and the −X side) of the MR sensor 147. Furthermore, thelongitudinal directions of the pressure spring 141 and the support plate161 are arranged to lie in the direction along the shifting direction ofthe scale 130, in other words of the rotating tube 105. In this manner,the longitudinal directions of the pressure spring 141 and the supportplate 161 are arranged to be disposed so as to be approximatelyorthogonal to the direction of the optical axis L, and thereby it ispossible to reduce the size or extent of the device along the directionof the optical axis L (the Y axis direction).

As has been explained above, according to this first embodiment, theholder 145 is supported by the support plate 161, and the pressure isapplied by the pressure spring 141. By doing this, it is ensured thatthe MR sensor 147 does not tilt with respect to the scale 130, so thatit is possible to obtain a sufficiently great detection signal.

Since the MR sensor 147 is fitted so as to have no play, it is possibleto read out the scale 130 accurately.

Since the shapes of the components, such as the pressure spring 141 andthe support plate 161, are made to be simple, accordingly it is possibleto manufacture these components easily, with high accuracy, and moreoverat low cost.

Second Embodiment

FIG. 4 is a perspective view showing a lens barrel 100A which isequipped with a displacement detection device according to the secondembodiment of the present invention. FIG. 5( a) is a figure showing thedisplacement detection device according to this second embodiment asseen from the outer peripheral side of the lens barrel 100A, while FIG.5( b) is a figure showing this displacement detection device as seenfrom the side of a subject to be photographed.

In FIGS. 4, 5(a), and 5(b), to portions which correspond to portionswhich have the same functions as ones in FIGS. 1, 2(a), and 2(b), thesame reference symbols are appended. In this displacement detectiondevice according to the second embodiment, in place of the support plate161 of the first embodiment discussed above, there is provided a supportplate 162 whose shape and arrangement have been altered. Here, theexplanation will focus upon the features which differs from the firstembodiment described above.

FIG. 6( a) is a figure showing a plan view of the support plate 161 ofthe first embodiment, while FIG. 6( b) is a figure showing a plan viewof the support plate 161 of this second embodiment. As shown in FIG. 6(a), the support plate 161 is made in a thin plate shape with an elasticcharacteristic, and the holder 145 is arranged below the support plate161. As shown in FIG. 6( b), the support plate 162 is formed in anelastic thin plate shape and has a hole portion 162 a pierced throughit, and the holder 145 is arranged above the support plate 162.

Since the support plate 161 of the first embodiment offered almost nosupport in the directions approximately orthogonal to the contact plane(the Z axis direction) as described above, accordingly the holder 145could be shifted in the Z axis direction by a small force. Thus, whenthe rotating tube 105 turned, sometimes an undulation was set up due tothe manufacturing inaccuracy of components constituting the rotatingtube 105 and the like, so that the contact position S wobbled in the Zaxis direction.

It has been considered to make the applied pressure force (the pressingforce) of the pressure spring 141 larger, so as to enable the holder 145accurately to follow the rotating tube 105, in other words the scale130, even if an undulation has been set up by the rotation of therotating tube 105. However, when the pressure force which is applied bythe pressure spring 141 becomes great, the sliding resistance betweenthe scale 130 and the MR sensor 147 becomes great, and this can becomean obstacle to the rotational driving of the rotating tube 105. In thisconnection, it is desirable to ensure that the following upcharacteristic of the holder 145 is excellent by making the supportforce in the Z axis direction due to the support plate 161 small.

In this connection, as shown in FIG. 6( b), the hole 162 a is providedin the central portion of the width (the Y axis direction) of thesupport plate 162, and thereby the rigidity of the support plate 162 isreduced, so that the support force in the Z axis direction is reduced.

FIGS. 7( a) through 7(d) are figures showing the contact situationbetween the holder 145 and the scale 130 with the tilt therebetweenexaggerated. It should be understood that the spacer film 149 and theflexible printed circuit 151 and so on have been omitted from thesefigures for sake of clarity.

As shown in FIGS. 7( a) and 7(b), if tilting of the rotating tube 105occurs due to the influence of manufacturing inaccuracies or the like,then the MR sensor 147 may come to contact with the scale 130 onlypartially with relation to the widthwise direction of the scale 130, inother words the shifting direction of the rotating tube 105, which isundesirable. At this time, as shown in FIGS. 7( c) and 7(d), the supportplate 162 is deformed in a twisting manner when pressure is applied asshown by the arrow A to the approximate center of the MR sensor 147, inother words the approximate center of the contact position S (refer toFIG. 3) where the MR sensor 147 and the scale 130 are properly contactedwith each other. Due to this, it is possible for the MR sensor 147 to betightly in contact with the scale 130, as shown in FIG. 7( d).

As shown in FIGS. 5( a) and 5(b), in this embodiment, a spherical convexportion 145 a is arranged in a position which corresponds to theapproximate center of the MR sensor 147, in other words to theapproximate center of the contact position S between the MR sensor 147and the scale 130. By the pressure spring 141 applying pressure to thisspherical convex portion 145 a, it is possible to apply pressure to theapproximate center of the contact position S of the MR sensor 147.

As has been described above, the hole 162 a is provided in the bentportion of the support plate 162, so as to reduce the rigidity of thesupport plate 162 in the Z axis direction. By doing this, it is possibleto shift the holder 145 along the Z axis direction with a smaller forceso that the MR sensor 147 can be tightly and reliably in contact withthe scale 130 with the spring force of the spring 141.

As shown in FIG. 6( b), the hole 162 a is provided at the centralportion of the support plate 162 in its widthwise direction (its Y axisdirection). If only the rigidity of the support plate 162 were to bereduced, it would be simple to reduce the width of this plate (i.e. itslength along the Y axis direction). However, it is necessary to hold theposition of the holder 145 in the direction of the contact plane (i.e.in the X-Y plane) accurately even when the resistance to deformation ofthe support plate 162 in the Z axis direction is reduced. Thus, in thissecond embodiment, by providing the hole 162 a in the central portion ofthe support plate 162, the rigidity in the direction of the contactplane is not greatly deteriorated, while the bending rigidity in the Zaxis direction is effectively reduced. Furthermore, due to the provisionof the hole 162 a, the beneficial result is also obtained that thetorsional rigidity of the support plate 162 is reduced.

As shown in FIG. 5( b), the position in which the support plate 162 isfitted is different from that of the support plate in the firstembodiment; it is provided in a position virtually on the contact plane.Due to this, the holder 145 is provided on the +Z axis side of thesupport plate 162, and is arranged so as to be sandwiched between thesupport plate 162 and the pressure spring 141.

FIG. 8 is a fictitious figure for explanation of a hypothetical case inwhich the support plate 162 of the second embodiment has been providedin the same position as was the support plate 161 of the firstembodiment. The support plate 162 of this second embodiment, asexplained above, always has less rigidity in the Z axis direction. Letus tentatively suppose that, the support plate 162 were to be arrangedas shown in FIG. 8 with the holder 145 being disposed upon the −Z sideof the support plate 162. In such a case, when the rotating tube 105rotated in the direction of the arrow R in the figure, the bendingmoment M which acted upon the support plate 162 due to the frictionalforce F at the contact position S would become large. Due to this, thesupport plate 162 might be deformed, which would be undesirable.However, the actual situation with the second embodiment is that, sincethe support plate 162 is provided in a position which is approximatelyon the contact plane, the bending moment becomes small and also it ispossible to prevent the occurrence of deformation.

As has been explained above, since, according to this second embodiment,the hole 162 a is provided in the support plate 162, accordingly it ispossible for the holder 145 to shift in the Z direction under a lighterforce. Due to this, it is possible to enhance the followingcharacteristic of the holder 145 even if undulations of the scale 130 orthe like should occur, without making the pressing force of the pressurespring 141 any greater, and thus it is possible to read the scale 130more accurately through the MR sensor 147.

Since the support plate 162 is provided in a position which comes to beapproximately on the contact plane, the bending moment which acts uponthe support plate 162 due to the rotation of the rotating tube 105becomes small. Due to this, it is possible to prevent undesirabledeformation of the support plate 162, even though the bending rigidityof the support plate 162 due to the provision of the hole 162 therein isreduced.

Variant Embodiments

Although the displacement detection device and the lens barrel of thepresent invention have been explained above in terms of first and secondembodiments thereof, they should not be considered as being limited bythe details of these embodiments; various changes to the form andcontent of any particular embodiment are possible, and these variantsare also to be considered as falling within the scope of the presentinvention.

For example while, in the above described embodiments, as an example,the method shown for fixation of the support plates 161 and 162 and theholder 145 was by way of adhesion, it is not limited to this method; forexample, it would also be acceptable to utilize thermal caulking, insertmolding, or some other fixing method.

Moreover although, by way of example, in the second embodiment, it wasdescribed that the hole 162 a was provided in the support plate 162, andmoreover that the support plate 162 was provided in a position which wasapproximately on the contact plane, the present invention is not to beconsidered as being limited by these constructional details. Forexample, it would also be acceptable to arrange the support plate, withthe hole 162 a pierced through it, in the same position as in the firstembodiment; or, conversely, it would also be acceptable to provide asupport plate formed with no such hole 162 a, in the same positionapproximately on the contact plane.

Although the spherical convex portion 145 a was provided in the holder145, it would also be acceptable, as an alternative, to utilize a convexportion which was formed as a polyhedron, provided that pressure wasapplied by the pressure spring 141 in the approximate center of thecontact position of the MR sensor 147. Furthermore, it would also bepossible to use a convex portion of which only a portion was formed in aspherical shape. Although, as shown in FIG. 5( a), due to the provisionof the hole 162 a, the support plate 162 is formed in a U shape, itwould also be possible, as an alternative, to form the support plate 162in a frame shape by providing a hole in its central portion.

Although the above described embodiments were described in terms of adisplacement detection device which detected the magnetism of the scale130 with the MR sensor 147, in other words in terms of a magneticencoder, it would also be possible to utilize a displacement detectiondevice in which a magnetic type scale was not used.

As has been explained above, with the displacement detection deviceaccording to the various embodiments of the present invention, thedisplacement detection section is supported so that the support plates161 and 162 are able to shift in the direction which is approximatelyorthogonal to the contact plane, while their shifting in directionsother than said direction which is approximately orthogonal to thecontact plane is restricted. Due to this it is possible to obtain asufficient detection signal, without the displacement detection sectionincluding the MR sensor 147, the spacer film 149, the flexible printedcircuit 151 and the like tilting with respect to the scale 130.Furthermore, it is possible to read off the scale accurately without anyplay occurring.

Since the support plates 161 and 162 are made as thin plate members withan elastic characteristic, they are cheap to manufacture.

Since the support plates 161 and 162 are fixed at their one ends to thefixing section 103 a, and support the holder 145 of the displacementdetection section by their other ends, accordingly it is possible tomake the support plates 161 and 162 of a simple structure.

Since the support plates 161 and 162 are arranged so that theirlongitudinal directions run along the direction of shifting of the scale130, it is possible to take advantage of the available spaceeffectively, and accordingly it is possible to make the displacementdetection device more compact. In particular, it is possible to reduceits size in the direction of the optical axis L.

Since the pressure spring 141 applies pressure approximately in thecenter of the contact position of the displacement detection section,accordingly the support plates 161 and 162 deform in a twisting mannerso that the displacement detection section follows the scale 130. Due tothis, it is possible to enhance the degree of contact between thedisplacement detection section and the scale 130, thus making itpossible to obtain an accurate detection value.

Since the support plates 161 and 162 are provided on the contact planeor in the vicinity of the contact plane, and are arranged as beingapproximately parallel to the contact plane, it is possible to preventthe support plates 161 and 162 from being deformed by the rotation ofthe rotating tube 105.

Since the support plate 162 comprises a rigidity reduction section at aportion which bends when the displacement detection section shifts inthe direction approximately orthogonal to the contact plane, accordinglyit is possible to enhance the following characteristic of thedisplacement detection section with respect to the scale 130. Since thisrigidity reduction section is provided in the vicinity of theapproximate center of the support plate 162, accordingly, along withreducing the rigidity in the direction which is substantiallyperpendicular to the contact plane, it is also possible reliably to holdthe position of the contact plane direction. And, since the rigidityreduction section is the hole portion 162 a which is provided in thesupport plate 162, accordingly it is easy and simple to construct.

Since the pressure spring 141 does not apply force to or restricts theposition of the displacement detection section in any direction otherthan the pressure application direction in which the displacementdetection section is pressed towards the scale 130, accordingly it ispossible to maintain the position of the displacement detection sectionaccurately.

Since the pressure spring 141 is arranged so that its longitudinaldirection runs along the direction of shifting of the scale 130,accordingly it is possible to take efficient advantage of the availablespace, and therefore it is possible to make the displacement detectiondevice more compact. In particular it is possible to reduce its sizealong the direction of the optical axis L.

Since the scale 130 is a magnetic scale of which the different magneticpoles are arranged alternatingly along the shifting direction, and thedisplacement detection section includes the magnetoresistive sensor 147which detects the magnetism of this magnetic scale, accordingly it ispossible to detect the displacement accurately. And, since the spacerfilm 149 is provided upon the portion of the magnetoresistive sensor 147which faces the magnetic scale 130, accordingly it is possible to ensurethe appropriate gap between the magnetoresistive sensor 147 and themagnetic scale 130, so that it is possible to perform the detection ofdisplacement accurately.

Since the convex portion 145 a is provided in the portion to whichpressure is applied by the pressure spring 141 of the displacementdetection section, accordingly it is possible for the displacementdetection section to apply pressure effectively so as to follow alongthe scale 130.

As has been explained above, in the lens barrel according to theembodiments of the present invention, there are comprised a photographicoptical system, the fixed tube 103 which is mounted to the photographicdevice main body, and the above described displacement detection device.This displacement detection device detects displacement of the movabletube 105 that rotates with respect to the fixed tube 103 so as to driveat least a portion of the photographic optical system. Due to this,along with it being possible accurately to detect the displacement ofthe movable tube 105, it is also possible to make the lens barrelparticularly compact along the direction of the optical axis. It is alsopossible to make the camera itself more compact by fitting a lens barrelof the type described above to the camera main body.

INDUSTRIAL APPLICABILITY

Although in the above the displacement detection device of the presentinvention has been explained, by way of example, in terms of itsapplication to a lens barrel, the present invention could also beapplied, in the same manner, to any other device for which accuracy ofdetection of displacement of a movable member was required.

1. A displacement detection device which detects a displacement of amovable member which is provided so as to be displaceable with respectto a fixed member, comprising: a scale that is provided as a unit withthe movable member; a displacement detection section that detects adisplacement of the scale; a support member that supports thedisplacement detection section in a state in which the displacementdetection section is able to shift in a direction which is substantiallyperpendicular to a contact plane where the displacement detectionsection contacts with the scale at a contact position between thedisplacement detection section and the scale and in which shifting in adirection other than the direction substantially perpendicular to thecontact plane is restricted; and a pressure application member thatapplies a pressure to the displacement detection section towards thescale.
 2. A displacement detection device according to claim 1, wherein:the support member is formed as a thin plate member with an elasticcharacteristic.
 3. A displacement detection device according to claim 1,wherein: one end of the support member is fixed to the fixed member, andanother end of the support member supports the displacement detectionsection.
 4. A displacement detection device according to claim 1,wherein: the support member is arranged so that a longitudinal directionthereof extends along a direction of shifting of the scale.
 5. Adisplacement detection device according to claim 1, wherein: thepressure application member applies the pressure substantially in acenter of the contact position of the displacement detection section. 6.A displacement detection device according to claim 1, wherein: a portionof the scale which contacts with the displacement detection section is atube surface, and the support member is provided on the contact plane orin the vicinity of the contact plane, and is arranged substantiallyparallel with the contact plane.
 7. A displacement detection deviceaccording to claim 1, wherein: the support member comprises a rigidityreduction section at a portion of the support member which bends whenthe displacement detection section shifts in the direction substantiallyperpendicular to the contact plane.
 8. A displacement detection deviceaccording to claim 7, wherein: the rigidity reduction section isprovided in the vicinity of a substantial center of the support member.9. A displacement detection device according to claim 7, wherein: therigidity reduction section is a hole portion which is provided in thesupport member.
 10. A displacement detection device according to claim1, wherein: the pressure application member does not apply force to thedisplacement detection section and does not restrict a position of thedisplacement detection section in a direction other than a pressureapplication direction in which the pressure application member appliesthe pressure to the displacement detection section towards the scale.11. A displacement detection device according to claim 1, wherein: thepressure application member is arranged so that a longitudinal directionthereof extends along a direction of shifting of the scale.
 12. Adisplacement detection device according to claim 1, wherein: the scaleis a magnetic scale whose different magnetic polarities are arrangedalternatingly along a shifting direction, and the displacement detectionsection comprises a magnetoresistive sensor that detects a magnetism ofthe magnetic scale.
 13. A displacement detection device according toclaim 12, wherein: the displacement detection section includes a gapregulation member that regulates a gap between the magnetoresistivesensor and the magnetic scale, and the gap regulation member is providedon a side of the magnetoresistive sensor which faces the magnetic scale.14. A displacement detection device according to claim 1, wherein: thedisplacement detection section comprises a convex portion at a portionthereof to which the pressure is applied by the pressure applicationmember.
 15. A lens barrel, comprising: a photographic optical system; afixed member that is to be fitted to a photographic device main body;and a displacement detection device which detects a displacement of amovable member which is provided so as to be displaceable with respectto a fixed member, that comprises (a) a scale that is provided as a unitwith the movable member; (b) a displacement detection section thatdetects a displacement of the scale; (c) a support member that supportsthe displacement detection section in a state in which the displacementdetection section is able to shift in a direction which is substantiallyperpendicular to a contact plane where the displacement detectionsection contacts with the scale at a contact position between thedisplacement detection section and the scale and in which shifting in adirection other than the direction substantially perpendicular to thecontact plane is restricted; and (d) a pressure application member thatapplies a pressure to the displacement detection section towards thescale, wherein: the displacement detection device detects a displacementof the movable member that rotates with respect to the fixed member todrive at least a portion of the photographic optical system.
 16. Acamera comprising: a camera main body, and a lens barrel that comprises;a photographic optical system, a fixed member that is to be fitted to aphotographic device main body, and a displacement detection device whichdetects a displacement of a movable member which is provided so as to bedisplaceable with respect to a fixed member, that comprises (a) a scalethat is provided as a unit with the movable member; (b) a displacementdetection section that detects a displacement of the scale; (c) asupport member that supports the displacement detection section in astate in which the displacement detection section is able to shift in adirection which is substantially perpendicular to a contact plane wherethe displacement detection section contacts with the scale at a contactposition between the displacement detection section and the scale and inwhich shifting in a direction other than the direction substantiallyperpendicular to the contact plane is restricted; and (d) a pressureapplication member that applies a pressure to the displacement detectionsection towards the scale, wherein the displacement detection devicedetects a displacement of the movable member that rotates with respectto the fixed member to drive at least a portion of the photographicoptical system.
 17. A displacement detection method that detects adisplacement of a movable member relative to a fixed member, the methodcomprising the steps of: mounting a scale on the movable member;providing a detector that is capable of contacting the scale to detect adisplacement of the scale; supporting the detector by a supportingmember, the supporting member movably supporting the detector in a firstdirection substantially perpendicular to a contact plane where thedetector contacts with the scale at a contact position and restricting amovement of the detector in a second direction other than the firstdirection; and applying a pressure to the detector toward the scale.